Metal surfaces can be protected and given an aesthetic appearance by the application of one or more coats of paint. Typically, two or more coats are usually applied. They may comprise
(1) a primer or basecoat to provide corrosion protection; PA0 (2) a topcoat to provide an aesthetic appearance. PA0 (i) electrophoretically applying a basecoat on the substrate, PA0 (ii) drying the substrate by baking the same over an effective temperature-time schedule to a stage short of complete cure so as to evaporate residual water and volatile material from the coating in order to effect reflow of said coating, PA0 (iii) non-electrophoretically applying a thermosetting fluid, high solids topcoat comprising isocyanate curing agents, PA0 (iv) curing the substrate by baking the same over a temperature-time schedule sufficient to effect complete cure.
The topcoating can be applied in a wet-on-wet mode, i.e., without first curing the basecoat, and with a minimum of flash time for the basecoat, before the topcoat is applied to the basecoat.
It has been found that the wet-on-wet mode of applying high solids fluid thermosetting topcoats leaves something to be desired as to the visual appearance and durability of the coated substrate. This is due seemingly to intermixing of the basecoat and topcoat and bubbling of the primer through the topcoat. This results in the creation of large surface crawling or cratering in the topcoat. To avoid the intermixing of the basecoat and topcoat, presumably less mixable coatings such as powder coatings have been employed as topcoatings. The present invention provides an improved wet-on-wet mode of coating which produces improved durability and appearance of the coated substrate.